Preparation of perfluoroacyl fluorides and perfluorocarboxylic acids

ABSTRACT

Pyrolysis of perfluoroalkanesulfonate salts of yttrium, scandium and rare earth metals in an inert atmosphere provides acyl fluorides when anhydrous salts are employed and carboxylic acids when the hydrated salts are employed. The acyl fluorides and carboxylic acids are useful intermediates known and used in the art.

llmted States Patent 1 1 [111 3,723,485 Thom 1*Mar. 27, 1973 [54]PREPARATION OF PERFLUOROACYL [56] References Cited FLUORIDES ANDPERFLUOROCARBOXYLIC ACIDS UNITED STATES PATENTS 3,254,107 /1966Houplschien et al. ..260/5 39 R [75 1 Invent Karl Paul 2,765,326 /1956Severson et al. ..260/544 F [73] Assignee: Minnesota Mining andManufacturmg Company Paul Primary Examiner-Henry R. Jiles Notice: Theportion of the term of this Assistant minerJ0hn F Terapane patentsubsequent to Oct. 26, 1988, y y Steldt and has been disclaimed. Dela-ht [22] Filed: Feb. 20, 1970 ABSTRACT [21] Appl. No.: 13,159

Pyrolysis of perfluoroalkanes'ulfonate salts of yttrium, RelatedApplicatiml Dam scandium and rare earth metals in an inert atmosphere 63C an f S N 872,726, provides acyl fluorides when anhydrous salts ere em-1 82; lfifi f gg E 0 t ployed and carboxylic acids when the hydratedsalts are employed. The acyl fluorides and carboxylic acids 52 US. Cl...260/408, 260/514 R, 260/539 R, are useful intermediates known and d inthe 260/539 A, 260/544 F I [51] Int. Cl. ..C07c 61/18, C 3/00 4 Claims,No Drawings [58] Field of Search ..260/539 R, 539 A,

PREPARATION OF PERFLUOROACYL FLUORIDES AND PERFLUOROCARBOXYLIC ACIDSThis application is a continuation-in-part of my copending U.S. Pat.application Ser. No. 872,726, filed Oct.30, 1969, now U.S. Pat. No.3,615,169.

This invention relates to a new process for the production ofperfluoroacyl fluorides and carboxylic acids from sulfonic acids havingthe same total carbon atoms. In particular it relates to a pyrolyticdecomposition of the rare earth, yttrium and scandium salts ofperfluoroalkanesulfonic acids.

Perfluoroacyl fluorides which could be converted to the correspondingperfluorinated carboxylic acids have heretofore been obtained largely bythe fluorination of the common aliphatic carboxylic acids'The earlyhistory of fluorine chemistry including descriptions of theelectrochemical fluorination processes of the alkanoic acids aredescribed in the book Fluorine Chemistry, edited by Dr. J. H. Simons,Academic Press, Inc. Publishers 1950. It is more convenient tofluorinate the sulfonic acids and the yields are generally considered tobe better. The conversion of the sulfonic acids to the perfluorinatedcarboxylic acids is now possible by the present process. There are, ofcourse, other possible routes to these carboxylic acids but, sofar as isknown, the present reaction is one which has neither been observed norwould it have been expected.

It is an object of this invention to provide a process for theproduction of perfluoroacyl fluorides and perfluorocarboxylic acids.Other objects will become apparent hereinafter.

lt hasbeen discovered quite unexpectedly that the pyrolysis of theperfluoroalkanesulfonates of scandium, yttrium and the rare earth metalsproceed by loss of sulfur dioxide, the formation of the metallicfluoride and at the same time there is formed a perfluoroacyl fluorideincluding the carbon atoms of the original perfluoroalkane group. Theacid has one less fluorinated carbon atom.

This is quite an interesting and unexpected reaction inasmuch as itinvolves the removal of a fluorine at tached to carbon and replacementby oxygen. lt also involves a cleavage of the sulfonic acid linkagewhich in itself is not to be expected.

The preparation of perfluoroacyl fluorides and perfluorocarboxylic acidsaccording to this invention is by heating from about 400 to l,000 C inargon as approximated by the following respective equations:

where M is a trivalent ion of rare earth metal, Y or Sc. Nitrogen orother inert gases may be used or alternatively pyrolysis may be carriedout under reduced pressure.

The perfluoroalkanesulfonate salts used in these reactions are describedin the parent hereof, Ser. No. 872,726, now U.S. Pat. No. 3,615,169, andhave the general formula:

(R,CF SO O) M.XH O

where M Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Xis an indefinite number up to about nine, and R, is a monovalentfluoroaliphatic radical of one to 20 carbon atoms. The fluoroaliphaticradical may contain not more than one hydrogen or I chlorine for twocarbons in the chain, such as omegahydroperfluoroalkyl andomega-chloroperfluoroalkyl. It may be an acyclic straight or branchedchain structure or a combination thereof or it may be cyclic orheterocyclic including one or more oxygen atoms each linking two carbonatoms or nitrogen atoms linking together three carbon atoms in either anacyclic or cyclic structure. The preferred fluoroaliphatic radical isperfluoroalkyl. Sofar as is known this provides a convenient process forconverting any fluoroaliphatic sulfonic acid to a fluoroaliphaticcarboxylic acid as shown in the above equations.

Examples of R, radicals include where R,is CF;, to C F and n is aninteger.

The salts, as produced, contain various amounts of water ofcrystallization which must be removed carefully by vacuum and/ormoderate heating if the perfluoroacyl fluoride is the desired product.Alternatively, the water liberated in pyrolysis must be carefullyseparated from the perfluoroacyl fluoride by trapping in a cold trap. Ifthe perfluorocarboxylic acid is the desired product, the water ofcrystallization merely hydrolyzes the acyl fluoride and need not beremoved.

The novel reaction is apparently restricted to salts of the trivalentrare earth metals, yttrium and scandium. Mixed cation salts may also beutilized and no deleterious effects are observed. That is, mixtures ofrare earth metal cations as present in mischmetall can be employed asobtained directly from ores. The divalent transition metalfluoroaliphatic sulfonate salts do not yield detectable quantities ofperfluoroacyl fluorides or carboxylic acids. Thus copper, cobalt andchromium are ineffective. The coordinated rare earth compounds (Wernercomplexes) described in the parent application do not yield the desiredacids or acid fluorides because the liberated ligands react with theacyl fluoride and complex mixtures are obtained.

In the most general practice of this invention, theperfluoroalkanesulfonic acid is selected as required for the desiredcarboxylic acid or acyl fluoride. This acid is reacted with rare earthoxide (or yttrium or scandium oxide) and the resulting salt recovered.Reaction may be carried out using an ore as described in my copendingapplication Ser. No. 872,726 now U.S. Pat. No. 3,615,169. Mixed rareearth oxide from decomposition of oxalates may be used or individualrare earths may be used as the oxides. The salt is dried and pyrolyzedand the perfluoroacyl fluoride recovered. If the perfluorocarboxylicacid isdesired, the salt need not be dried and a small amount of watermay even be added to hydrolyze the perfluoroacyl fluoride as formed.

Having described the invention in general terms it is now morespecifically described in examples.

EXAMPLE 1 Neodymium salts are prepared by the above procedure usingperfluorobutanesulfonic acid, perthe apparatus and the leg containingthe salt is heated at 600 C for one hour. After pyrolysis and coolingthe apparatus, moist air is admitted. The product is identified byboiling point and IR spectrum as C F, CO

fluorohexanesulfonic acid, perfluoroethylcyclohex- 5 H. An 80 percentyield of the acid is obtained, anesulfonic acid, perfluoroethanesulfonicacid, [3- The following Examples 5 to 9 are run in the samehydroperfluoropentanesulfonic acid (C F Cl lFCF manner as Example 4above. The results are sum- SO H), and B-hydroperfluoroethanesufonicacid marized in Table l.

V TABLE 1 Vacuum Rare earth salt pyrolysis Product v xlfldm, n.0, 'iifij' ffiiiti 151*. o v. Perr -n1 Example Formula gm. percent hourIdentification at, 740 llllll. yiv

5 N(1(SO3COFU)3 u 700 1 o in: m

CSFH QLoIL o Mixed R.E. 20 as 800 1 o 100 7a (SO3CdFi3)3 C5F(|E )1I 7soloing; 20 5.8 700 1 o 100 54 CSFM LOH 8 Nd(SO3C5F17)3 20 l 7 700 1 U18" 73 (maid-011 0 20 4. 5 700 1 o 1210 so Nd(S0 C2F F 1L 3 1 c1 2c-oii(CHF CF SO H). These neodymium salts are dried and What is claimed is:portions decomposed in argon at 800 C. to give pure 3O 1. The processfor the preparation of perfluoro-carneodymium fluoride. Theperfluorobutane and perboxylic acids or acid fluorides comprisingfluorohexane groups are recovered in part as perheating yttrium,scandium or rare earth trivalent fluoropropionic and perfluorovalericacids respectivemetal Sa t o combinations thereof, of fluor ly.aliphatic sulfonic acid having the formula:

Other lanthanide metals and group 3b metals are also R F so H convertedto trifluoromethane sulfonates, the salts 1C 2 3 pyrolyzed and thefluorides recovered. Suitable metals h i R, i fl li h i di l of 1 20carbon (in trivalent form) are cerium, praeseodymium, atoms of the groupof: promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, 40 lutecium, yttrium, scandium.(CFz) These various fluoroaliphatic sulfonate salts form hydrates. F F

EXAMPLE 2 and Neodymium perfluoromethanesulfonate is prepared from theoxide and sulfonic acid. 10 grams of this salt i are placed in analumina boat and the boat and salt are F then placed in a Pyrex tubularfurnace. Nitrogen gas is wherein is CFa to used to sweep out thevolatile products during thermal decomposition Of the Salt (800 C 4hours). The volatil- C3F7 and n is an integer for a ufficient for gasized products are collected in traps immersed in evolution to come to ahalt at a temperature of nitrogen. Infrared analysis of the gasesidentifies COF about 400 to 1 000 C, il condensing ff. and 2- gaseswhereby perfluoroacyl fluorides are recovered under EXAMPLE 3 anhydrousconditions and perfluoro-carboxylic Neodymium erfluoroethane ulfonate id acids are recovered when water vapor is present. posed similarly at600 C for 1 hour in nitrogen to give 2. The process of claim 1 whereinthe salts are perfluoroacetyl fluoride. hydrated and carboxylic acidsare recovered from the condensate. EXAMPLE 4 3. The process of claim 1wherein the salts are essen- Neodymium perfluorooctanesulfonate (10 gm.)is tially anhydrous and the carboxylic acid fluorides are prepared asdescribed above. The salt is pyrolyzed in an recovered from thecondensate. inverted U-shaped apparatus having a detachable leg 4. Theprocess according to claim 1 wherein R, is a provided with a glass woolplug inserted above it. The apparatus is evacuated to one micron. ADewar flask containing liquid nitrogen is placed on the other leg ofperfluoroalkane group C E

2. The process of claim 1 wherein the salts are hydrated and carboxylicacids are recovered from the condensate.
 3. The process of claim 1wherein the salts are essentially anhydrous and the carboxylic acidfluorides are recovered from the condensate.
 4. The process according toclaim 1 wherein Rf is a perfluoroalkane group CnF2n 1.